This invention relates to improvements in pins of the type used in coupling mechanical parts together. Typical applications include the keying of sprockets, gears, etc. to shafts. Pins of the foregoing type are ordinarily driven into a circular hole that is formed in the mechanical member to which the pin is attached. These holes have a fairly wide range of tolerances regardless of whether or not they are drilled, punched or cored. Furthermore, the tolerance normally increases as the function of the diameter of the hole. Accordingly, spring and serrated pins of the various designs have come into widespread use in order to accommodate for these tolerances.
Ideally, there should be a close tolerance between the hole and the pin. To accomplish this it is possible to form the hole by reaming or honing and to provide a precision ground pin of circular cross section to fit therein. While structurally desirable, such an arrangement is rather expensive.
Another problem of pins with circular cross section lies in the fact that circular pins in circular holes cause a sustained "hoop" stress that sometimes leads to cracking and bursting of the material around the hole. This, of course, is highly undesirable, particularly for applications involving dynamic loading. Moreover the hoop stress is accentuated if the pin is of maximum tolerance and the hole is of minimum tolerance.